1. Field of the Invention
This invention relates to photographic lenses having a motor therein, and more particularly to a technique of moving the diaphragm blades stepwise by a stepping motor.
2. Description of the Prior Art
Mechanical devices for operational control of a diaphragm device in a lens barrel have found wide acceptance.
Such a structure has, as illustrated in FIG. 1, two pivot pins on one end of each of a plurality of diaphragm blades. Only one of the diaphragm blades is shown. One of the pair of pins is rotatably fitted in a stationary portion (not shown) of the diaphragm device, and the other is freely fitted in an elongated slot 2a of a control member 2. The control member 2 has an axially extending arm portion 2b and is arranged to be rotatable relative to the aforesaid stationary portion, so that when the aforesaid arm portion 2b turns about the optical axis, as the pivot pins move in their respective slots, the diaphragm blades are caused to pivot to change the size of opening.
The control mode for determining the exposure, may be either the aperture priority and shutter time priority mode. In either of these control modes, the various factors for the exposure such as object brightness, film sensitivity, shutter time and aperture value are electrically processed by a computer system.
Present and future control systems for cameras are expected to employ electrical control as the method for meeting the demand for increased speed and accuracy.
But presently such electrical controls are located in the camera body, rather than in the lens. Proposals for incorporating an automatic focusing device in the photographic lens and for motorizing the zoom lens have been made. The conventional photographic lenses with motors built in are not compact, as they employ an ordinary motor and a drive connection which includes a gear train beween the output shaft of the motor and the movable member of the photographic lens.
It is known to build an electromagnetic drive into the diaphragm device for driving and controlling the diaphragm blades as, for example, in U.S. Pat. No. 3,687,042.
These diaphragm devices increase the number of constituent parts common to the diaphragm device and the electromagnetic mechanism. Thus, the device as a whole is increased in complexity, bulk and size.